1. Field of the Invention
This invention relates to a vehicle suspension system, and more specifically to an improvement in a suspension system of the double wishbone type.
2. Description of the Prior Art
Conventionally, it has been known, for example, from Japanese Unexamined Utility Model Publication No. 56(1981)-62207, that when a vehicle suspension system of the double wishbone type is applied to a front-engine and front-drive type vehicle, an A-type arm, formed by bending a piece of plate material into the shape of the letter "A", is employed for a suspension lower arm in place of an I-shaped arm so as to improve the rigidity since a suspension lower arm in the form of a letter "I", arranged in a manner to permit a drive shaft to pass therethrough, has low rigidity against lateral loads.
However, with the suspension system in which a suspension lower arm is formed by bending a piece of plate material, if the plate material is made thinner in thickness for reduction of weight, the suspension lower arm becomes less rigid at those portions thereof which require relatively high rigidity, including the portion thereof to which is attached a shock absorber at its lower end, the portion on which is mounted a ball joint, and the portion against which a stopper rubber abuts for restraining the up-and-down swinging motions of the suspension lower arm, and on the other hand, should the thickness of the suspension lower arm be made greater for enhanced rigidity, the total weight thereof becomes greater, thus precluding the weight reduction.
Also, in the above-described construction of the suspension system, a torsion bar is disposed in a manner such that it is aligned at its one end with an axis about which the suspension lower arm is caused to swing up and down. As a result, the mounting position of the torsion bar is necessarily lowered and hence a protector is required for preventing small stones or pebbles thrown up from the road surface from striking against the torsion bar and reducing its durability. However, the provision of the protector is disadvantageous in that it further reduces the ground clearance of the vehicle. Further, the torsion bar extends rearwardly to pass just over a rearwardly disposed cross member of a closed cross-sectional structure with a limited clearance formed therebetween, as a consequence of which it is necessary to lower the position of the cross member or to decrease the cross-sectional area thereof in order to avoid the interference of the suspension lower arm with the cross member as would occur upon swinging motion of the suspension lower arm.